1. Field of the Invention
The present invention relates to a scanning apparatus, and, more particularly, to a method and apparatus to compensate for imperfect scanner motion.
2. Description of the Related Art
A scanning apparatus is used to optically scan documents to generate corresponding image data. Such image data may be forwarded, for example, to an imaging apparatus, such as a printer, or may be transferred to another device, such as a computer or facsimile device.
One such scanning apparatus, commonly referred to as a flatbed scanner, typically controls and/or measures motion associated with the scanner at the scan motor, thereby allowing gear and belt imperfections of the scanner drive train to adversely impact scan quality. These mechanical imperfections cause low frequency errors, in the direction of scanner travel, that tend to be very repeatable for any particular scanner. Low frequency errors directly affect MTF scores (a common metric for scan resolution), and additionally on CCD (charge coupled device) scanners, also affect color registration. The end result is decreased scan quality and/or increased part cost. Traditionally gear accuracy has only been a concern for open-loop systems (step motor). However, since many closed-loop scanner systems (e.g., a DC motor driven system) utilize an encoder attached to the motor, transmission accuracy is equally important for both types of systems.
Thus, it is desirable to reduce the occurrence of scanning errors caused by variation in components of the scanning apparatus, such as due to manufacturing tolerances of one or more of components of the scanner drive train, e.g., gears, of the scanning apparatus.
What is needed in the art is method and apparatus to compensate for imperfect scanner motion.